They’re both flawed in very different ways.
Tyranny is much better at being an RPG in the dialogue heavy tradition of Obsidian or old BioWare; it has great worldbuilding, good writing (YMMV), and some terrific C&C, but the combat is forgettable at best and character progression is meh. If you play RPGs mainly for the combat or the systems, it’s not for you. That said, I think Tyranny very much knows what it does best and focuses on giving the player a lot of that. The game’s flaws would be far more forgivable if they’d had the resources to finish the damn ending. A storyfag game can get away with shit combat, it can’t get away with a botched and truncated third act. Even so, I replayed it immediately upon completion because I’m addicted to RPG reactivity and it absolutely scratches that itch.
I thought Pillars 3.0 was okay, but it’s almost the inverse of Tyranny: it has really good character progression and build variety, okay combat, but aside from MCA’s characters the story and the writing mostly get in the way.
Unlike Tyranny, though, Pillars devotes way too much effort to things it does poorly. Pillars could’ve been a damn good spiritual successor to Icewind Dale 2, but obviously that’s not the game people were clamoring for. It’s like the guy who made IWD2 tried to shoehorn a lot of dialogue and side quests and story into a title that plays more like a party based dungeon crawl. Oh wait, that’s exactly what happened.
Tyranny feels unfinished—one big gripe with the game is that there’s not enough of it. Pillars feels schizophrenic from a design perspective. It tries too hard to appease both storyfags and combatfags but ends up satisfying neither.
I’ll say this: Sawyer seems to have learned his lesson because Deadfire is a hell of a lot tighter. They added some high quality exploration, which is something the original Pillars really lacked, the writing is a lot less verbose, the combat has much better encounter design (far fewer trash mobs), there’s a lot of flexibility in the quests, and the faction system has genuine depth to it (at least this is my impression about a dozen hours in). The writing is definitely worse, but there’s a lot less of it and Sawyer isn’t using the great gobs of text as a crutch to tell the story.